1. Field of the Invention
The present invention relates to a power supply apparatus and printing apparatus, and particularly to a power supply apparatus and printing apparatus, which use a so-called back-boost type DC-DC converter and, more specifically, have a function of relaxing an output voltage rise caused by an abrupt decrease in load current.
2. Description of the Related Art
Conventionally, various methods have been proposed to cope with abrupt variations of a load current in a DC-DC converter.
For example, Japanese Patent Laid-Open No. 2005-020927 has proposed a method of detecting a drop voltage of an output voltage per unit time, and additionally inputting an electric power required to compensate for the drop voltage.
Also, Japanese Patent Laid-Open No. 2005-130616 has proposed a method in which a signal that can inform the power supply side of an abrupt change of a load current is provided on the load side, and the power supply side adjusts a reference voltage based on that signal.
Furthermore, Japanese Patent Laid-Open No. 2009-044448 has proposed a method of stopping a power supply output immediately before a load current decreases abruptly so as to relax an output voltage rise caused by the abrupt decrease in load current, which occurs during a power supply output stop process.
However, since most of these proposals aim at controlling output voltage variations caused by abrupt variations of a load current to fall within a given range on either the plus or minus side, the circuit arrangement and control method are complicated very much.
For example, in the method disclosed in Japanese Patent Laid-Open No. 2005-020927, a detector which detects a drop voltage of an output voltage per unit time, and a conversion table which is use for converting the detection result into an output duty ratio are required.
Also, in the method disclosed in Japanese Patent Laid-Open No. 2005-130616, a circuit which adjusts a reference voltage according to a change amount of a load current is required.
On the other hand, although the circuit arrangement and control method of Japanese Patent Laid-Open No. 2009-044448 are very simple, this method cannot be applied when a power supply output cannot be stopped at a timing immediately before an abrupt decrease in load current.